For Prime members only, Amazon offers the First Alert Motion-Sensing Light Socket for $9.49 with free shipping. (Walmart offers it for the same price via pickup.) That's tied with our June mention and the lowest price we could find by $8. It senses movement in all directions and can be used with 25- to 100-watt incandescent or CFL bulbs.

Update: The price has dropped to $8.60 at Walmart with in-store pickup. Amazon is pennies more.